program operatii;
var f,g:text;
    v:array[1..1000000]of 0..1000001;
    n,i,max,c,co:longint;
begin
assign(f,'operatii.in');
assign(g,'operatii.out');
reset(f);
rewrite(G);
read(f,n);
for i:=1 to n do
  read(f,v[i]);
i:=1;
while (i<=n)do
  begin
    max:=0;
    co:=0;
    while (v[i]<>0) do
      begin
        co:=co+1;
        if(v[i]>max)then max:=v[i];
        i:=i+1;
      end;
    c:=c+max;
    if (co=0)then i:=i+1;
  end;
write(g,c);
close(f);
close(g);
end.